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Nickelates are a rich class of materials, ranging from insulating magnets to superconductors. But for stoichiometric materials, insulating behavior is the norm, as for most late transition metal oxides. Notable exceptions are the 3D perovskite LaNiO 3 , an unconventional paramagnetic metal, and the layered Ruddlesden-Popper phases R 4 Ni 3 O 10 , (R = La, Pr, Nd). The latter are particularly intriguing because they exhibit an unusual metal-to-metal transition. Here, we demonstrate that this transition results from an incommensurate density wave with both charge and magnetic character that lies closer in its behavior to the metallic density wave seen in chromium metal than the insulating stripes typically found in single-layer nickelates like La 2- x Sr x NiO 4 . We identify these intertwined density waves as being Fermi surface-driven, revealing a novel ordering mechanism in this nickelate that reflects a coupling among charge, spin, and lattice degrees of freedom that differs not only from the single-layer materials, but from the 3D perovskites as well. Layered Ruddlesden-Popper structure nickelates R 4 Ni 3 O 10 ( R  = La,Pr) show an unusual metal-to-metal transition, but its origin has remained elusive for more than two decades. Here, the authors show that this transition results from intertwined density waves that arise from a coupling between charge and spin degrees of freedom

Superconductivity in FeSe emerges from a nematic phase that breaks four-fold rotational symmetry in the iron plane. This phase may arise from orbital ordering, spin fluctuations or hidden magnetic quadrupolar order. Here we use inelastic neutron scattering on a mosaic of single crystals of FeSe, detwinned by mounting on a BaFe2As2 substrate to demonstrate that spin excitations are most intense at the antiferromagnetic wave vectors QAF = (±1, 0) at low energies E = 6–11 meV in the normal state. This two-fold (C2) anisotropy is reduced at lower energies, 3–5 meV, indicating a gapped four-fold (C4) mode. In the superconducting state, however, the strong nematic anisotropy is again reflected in the spin resonance (E = 3.6 meV) at QAF with incommensurate scattering around 5–6 meV. Our results highlight the extreme electronic anisotropy of the nematic phase of FeSe and are consistent with a highly anisotropic superconducting gap driven by spin fluctuations.Extreme electronic anisotropy is revealed in the high-temperature superconductor FeSe through tour de force experiments on detwinned crystals.

SignificanceThe exactly solvable Kitaev model of bond-dependent near-neighbor interactions has drawn attention to quantum spins on the honeycomb lattice. But exotic quantum magnetism may also arise from competing interactions beyond nearest neighbors. Combining state-of- the-art theory and neutron scattering, we show that ferromagnetic nearest-neighbor interactions between effective spin-1/2 Co2+ spins in BaCo2(AsO4)2 are frustrated by antiferromagnetic third neighbor interactions. While an in-plane field suppresses the resulting incommensurate order, a ĉ−oriented field enhances quantum fluctuations. The spin Hamiltonian that we obtain will inform the search for quantum spin liquid physics in BaCo2(AsO4)2 subjected to tilted fields. Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid (KSL) state. One of the front-runners is BaCo2(AsO4)2 (BCAO), where it was suggested that the exchange processes between Co2+ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze a comprehensive inelastic neutron scattering (INS) study of BCAO with fields in the honeycomb plane. Combining the constraints from the magnon excitations in the high-field polarized state and the inelastic spin structure factor measured in zero magnetic field, we examine two leading theoretical models: the Kitaev-type JKΓΓ′ model and the XXZ-J1-J3model. We show that the existing experimental data can be consistently accounted for by the XXZ-J1-J3model but not by the JKΓΓ′ model, and we discuss the implications of these results for the realization of a spin liquid phase in BCAO and more generally for the realization of the Kitaev model in cobaltates.

Background With the aging of the population, frailty has attracted much attention, and the social dimension of frailty, namely social frailty, has also attracted attention. Studies have shown that social frailty can bring some adverse effects to the elderly, such as physical and cognitive function. Aims To explore the risk of adverse health outcomes in older adults with social frailty compared with older adults with non-social frailty. Methods Five databases were systematically searched from inception to February 28, 2023. Screening, data extraction and quality assessment were conducted independently by two researchers. The included studies were longitudinal studies of adverse outcomes in community-dwelling socially frail older adults, and the quality of each study was assessed using the Newcastle‒Ottawa Scale. Results A total of 15 studies were included based on the inclusion criteria, of which 4 were subjected to meta-analysis. The mean age of the included population ranged from 66.3 to 86.5 years. According to existing research, social frailty was predictive of some adverse outcomes, such as incident disability, depressive symptoms, and reduced neuropsychological function. The meta-analysis showed that social frailty had a significant predictive effect on mortality among older adults [HR = 2.27, (95% CI = 1.03–5.00)]. Conclusion In community-dwelling older adults, social frailty was a predictor of mortality, incident disability, depressive symptoms and other adverse outcomes. Social frailty had a negative impact on older adults, so it was necessary to strengthen the screening of social frailty to reduce the incidence of adverse outcomes.

Objective This systematic review examined studies that assessed the relationship between mortality risk and multidimensional frailty. The pooled risk of mortality was estimated via a meta-analysis. Design A systematic review and meta-analysis. Methods A systematic search for potentially eligible literature was conducted on January 2, 2023, using five electronic databases: Web of Science, CINAHL, PubMed, the Cochrane Library and Embase. This review included cohort or longitudinal studies examining the association between multidimensional frailty/prefrailty and mortality in older adults. The quality of the included studies was evaluated via the Quality in Prognosis Studies (QUIPS) tool. Two independent researchers identified eligible studies and extracted the data. The data analyses were performed via STATA, version 15.0. Results A total of 24 studies with 34,664 participants were included. The 24 studies were published between 2012 and 2022, with most studies being performed in Italy ( n  = 16). The sample sizes of the included studies ranged from 71 to 12,020. Most included studies were conducted in hospital settings. The QUIPS bias assessment results showed that the most frequent source of potential bias was study confounding. The meta-analysis results showed that multidimensional frailty was a significant predictor of mortality (HR = 5.48, 95% CI = 3.91–7.67, p  < 0.001). In addition, multidimensional prefrailty was also a significant predictor of mortality (HR = 2.56, 95% CI = 2.17–3.02, p  < 0.001). The results of the meta-analysis using the ORs revealed that multidimensional frailty was a risk factor for mortality in older people (OR = 4.59, 95% CI = 2.47–8.55, p  < 0.05). Conclusions and implications This systematic review of the relationship between multidimensional frailty and mortality found that multidimensional frailty/prefrailty is a predictor of mortality. More studies should be conducted in community dwelling populations and nursing homes.

The presence of a Higgs amplitude mode is revealed in a two-dimensional spin-half quantum antiferromagnet, C 9 H 18 N 2 CuBr 4 by means of neutron scattering. Spontaneous symmetry-breaking quantum phase transitions play an essential role in condensed-matter physics 1 , 2 , 3 . The collective excitations in the broken-symmetry phase near the quantum critical point can be characterized by fluctuations of phase and amplitude of the order parameter. The phase oscillations correspond to the massless Nambu–Goldstone modes whereas the massive amplitude mode, analogous to the Higgs boson in particle physics 4 , 5 , is prone to decay into a pair of low-energy Nambu–Goldstone modes in low dimensions 2 , 6 , 7 . Especially, observation of a Higgs amplitude mode in two dimensions is an outstanding experimental challenge. Here, using inelastic neutron scattering and applying the bond-operator theory, we directly and unambiguously identify the Higgs amplitude mode in a two-dimensional S = 1/2 quantum antiferromagnet C 9 H 18 N 2 CuBr 4 near a quantum critical point in two dimensions. Owing to an anisotropic energy gap, it kinematically prevents such decay and the Higgs amplitude mode acquires an infinite lifetime.

National user facilities such as the NIST Center for Neutron Research (NCNR) require a significant base of software to treat the data produced by their specialized measurement instruments. There is no universally accepted and used data treatment package for the reduction, visualization, and analysis of inelastic neutron scattering data. However, we believe that the software development approach adopted at the NCNR has some key characteristics that have resulted in a successful software package called DAVE (the Data Analysis and Visualization Environment). It is developed using a high level scientific programming language, and it has been widely adopted in the United States and abroad. In this paper we describe the development approach, elements of the DAVE software suite, its usage and impact, and future directions and opportunities for development.

Background Disease-modifying therapies (DMTs) that prevent immune cell infiltration into the brain have demonstrated efficacy in multiple sclerosis (MS) treatment. However, their unpredictable adverse effects necessitate the development of safer therapeutic alternatives. The choroid plexus (ChP) functions as a crucial barrier against immune cell invasion, and previous studies have shown that preventing immune cell infiltration across the ChP reduces brain lesion in MS animal models. Understanding ChP barrier regulation is therefore essential for identifying novel therapeutic targets for MS. Here, we explored the role of Ste20-related proline/alanine-rich kinase (SPAK) in experimental autoimmune encephalomyelitis (EAE). Methods We examined the expression patterns of SPAK signaling in ChP using immunofluorescence in the EAE model. To investigate the roles of SPAK, matrix metalloproteinase (MMP) 2 and MMP9 in EAE pathology, we performed ChP-specific gene manipulation via intracerebroventricular (ICV) injection of recombinant adeno-associated virus 2/5 (rAAV2/5). T cell infiltration into the central nervous system (CNS) was analyzed using CD4 immunostaining and flow cytometry. We employed cell immunofluorescence, transwell assays, and rescue experiments in vitro to study SPAK’s effects on ChP epithelial barrier integrity. We also evaluated the protective effects of SPAK-Na-K-2Cl cotransporter-1 (NKCC1) inhibitors (ZT-1a and bumetanide) on immune invasion and demyelination during EAE using pharmacological approaches. Results Following EAE induction, we observed progressive increases in both total and phosphorylated SPAK levels in ChP epithelium. Notably, ChP-specific SPAK knockdown significantly reduced T cell invasion and ameliorated EAE pathology, while SPAK overexpression exacerbated these effects. Bulk RNA sequencing and subsequent qPCR validation revealed that SPAK knockdown decreased the expression of MMP2 and MMP9, MMPs that compromise barrier integrity by degrading tight junction proteins. In vitro studies demonstrated that SPAK overexpression impaired ChP barrier function through the activator protein-1 (AP-1)-MMP2/9-zonula occludens-1 (ZO-1) axis. Furthermore, ChP-specific knockdown of either MMP2 or MMP9 protected against EAE pathology. Additionally, we identified SPAK-NKCC1 antagonists (bumetanide and ZT-1a) as promising therapeutic candidates for MS/EAE treatment. Conclusions Our findings demonstrate that targeting ChP-SPAK signaling represents a novel therapeutic strategy for MS treatment.

Quantum phase transitions in quantum matter occur at zero temperature between distinct ground states by tuning a nonthermal control parameter. Often, they can be accurately described within the Landau theory of phase transitions, similarly to conventional thermal phase transitions. However, this picture can break down under certain circumstances. Here, we present a comprehensive study of the effect of hydrostatic pressure on the magnetic structure and spin dynamics of the spin-1/2 ladder compound C 9 H 18 N 2 CuBr 4 . Single-crystal heat capacity and neutron diffraction measurements reveal that the Néel-ordered phase breaks down beyond a critical pressure of P c  ∼ 1.0 GPa through a continuous quantum phase transition. Estimates of the critical exponents suggest that this transition may fall outside the traditional Landau paradigm. The inelastic neutron scattering spectra at 1.3 GPa are characterized by two well-separated gapped modes, including one continuum-like and another resolution-limited excitation in distinct scattering channels, which further indicates an exotic quantum-disordered phase above P c . There is a class of quantum phase transitions that do not fit into the traditional Landau paradigm, but are described in terms of fractionalized degrees of freedom and emergent gauge fields. Hong et al. find evidence of such a transition in a molecular spin-1/2 antiferromagnetic ladder compound under hydrostatic pressure.

The grain boundary diffusion (GBD) process is currently the relatively effective method for utilizing heavy rare earth (HRE) elements in NdFeB magnets, especially for magnetic sheets. However, due to a highly uneven microstructure, the recovery of GBD magnets was considered difficult. In this work, our study prioritized short-loop recycling of GBD NdFeB sheet magnets to prepare block magnets. A comparative investigation was conducted between GBD-processed NdFeB magnets and the conventional sintered magnets, with particular emphasis on their recyclability characteristics. Among them, the Tb content of GBD magnets of 0.4 wt.% was significantly lower than sintered magnets of 1.73 wt.%. When two waste magnets were supplemented with the same amount of rare earth, it was found that the coercivity of the block magnets regenerated from GBD sheet magnets was higher. Microstructural analysis revealed that the core–shell grains originally located in the surface layer of GBD magnets were uniformly mixed and diffused with the ordinary particles originally located inside during the regeneration sintering process. The regenerated GBD magnets exhibited a more uniform core–shell microstructure with submicron shells of Tb elements along with reduced areas of RE-rich phase enrichment which facilitated the formation of a continuous and uniform thin-layer grain boundary, thereby enhancing the magnetic isolation effect. Apart from the significance of recycling, these block magnets regenerated from GBD magnets also provides a new approach to solving the challenge of high coercivity and low HRE elements in bulk magnets.